The present invention relates generally to the field of explosives and more particularly to means, known as detonators, used to detonate secondary explosives. More particularly, the present invention relates to an exploding thin film bridge fracturing flyer detonator for detonating secondary explosives.
It is well known that the passage of an electric current through a conductor generates a certain amount of heat, the amount of heat varying directly with the resistance of the conductor and with the square of the current. This phenomenon is relied upon in fusible links that are installed in electrical circuits to prevent the flow of more than a predetermined amount of current in such a circuit. When the predetermined flow is exceeded, the heat melts the fusible link so that the circuit is broken. If a sufficient current is passed through the link in a small period of time, the link is not only melted but may be vaporized. If the fusible link is enclosed in a small space the vaporizing of the link can increase the pressure in that space.
The blasting caps include a heat sensitive primary explosive set off by an electrical resistance heated by the passage of an electric current through the resistance. The exploding bridge wire devices detonate a primary explosive using a relatively low resistance bridge extending between conductors and through which a relatively high current is passed so that the bridge portion is not only heated to its melting point but is heated so much that it vaporizes and literally explodes to provide a shock wave to detonate the primary explosive. While such a system can use a primary explosive that is much less sensitive to heat and shock than a secondary explosive, there are still a distressing number of accidents that occur when the primary explosive is prematurely detonated, such a system does not provide the kinetic energy necessary to achieve reliable initiation of secondary explosives. Accordingly, a need exists for a more reliable and safe means for initiating secondary explosives.
Traditional exploding foil initiators, otherwise known as slappers, function by passing sufficient current through a metal foil or other conductor as to cause that material to vaporize. The pressure of this vaporization in concert with other vaporization phenomena cause a plate or disk to be driven to an acceptor explosive (i.e., a secondary explosive). The physical impact of this flying plate is such as to cause the explosive to be shock initiated. These devices have typically been constructed using materials for the flying plates which are organic or insulating layer which are organic. These organic materials have been limited to those that yield plastically before fracturing. This causes the effective surface area of the flying plate to be reduced by the amount of plastic deformation, otherwise known as the bubble effect.
Recently, it has been proposed to detonate these more stable explosives by an electrical means of some sort that creates a sudden pressure to shear a film and form a disk or flyer which is then impacted against the explosive material
One such example is disclosed in U.S. Pat. No. 4,602,565 (which is incorporated herein by reference) wherein an exploding foil detonator uses an explosive that is detonated by a flyer that is sheared form a sheet or film and propelled through a barrel to impact the explosive. The flyer is sheared from the sheet by the pressure generated when an electrical conductor adjacent the sheet is vaporized by the sudden passage of a high current (as by the discharge of a capacitor) through it. While this and other patents talk of the flyer being sheared this shearing does not occur until the material has experienced plastic deformation for the organic materials used to date, i.e. parylene and polymide. This plastic deformation, i.e., bubble effect, that occurs prior to shearing has the undesirable affect of reducing the effective surface are of the flyer. This reduction in flyer impact area reduces the kinetic energy transfer. This effectively reduces the likelihood that the impact will detonate a given explosive.
Organic compounds, e.g. parylene and polyamide, which have been used to date for the flyer and/or the insulating layer of prior art have susceptibility to the promotion of fungus growth and present considerable complexity to material compatibility, especially explosive compatibility analysis, due to both the complexity of their make up and the complexity of the chemical process and resulting chemical residue from their deposition.
As is typical in the prior art, the capacitor is in a circuit with the exploding thin film fracturing fragment detonator and a normally open switch. When it is desired to arm the system, the capacitor is charged, e.g., to 1000 volts; when it is desired to initiate the explosion, the switch is closed and the capacitor discharges through the thin film vaporizing the same.